Expulsion fuse



Feb. .19, 1935. l B. R. HERMANN Inventor.: Benjamin R. Her-m nn,

is i

EXPULSIQN E USE Filed oct. 6, 1955 Y Y Figi. Y'

Patented Feb. 199 1935 EXPULSION FUSE Benjamin R. Hermann, Pittsfield, Mass., assigner to General Electric Company, a corporation of New York Application October 6, 1933, Serlal No. 692,415 6 Claims. (Cl. 20D- 135) My invention relates to an expulsion fuse, more particularly to an expulsion fuse in which a small bore tube closely surrounds the fusible element. In the combination of expulsion fuses with line switches which are adapted to open upon operation of the fusible element, it is necessary for the fuse to be under tension to hold the switch in the closed position as long as the fusible element is intact and to release the switch upon operation of the fuse. It is impossible for the fusible element itself to withstand any tension and so it is necessary. to provide some means for relieving the fusible element of tension until operation of the fuse. It is important in providing means for relieving the fusible element of tension that the means provided for this purpose shall not interfere with the proper operation of the fuse.

An object of my invention is to provide an improved expulsion fuse in which the fuse may withstand a considerable tension and which will operate certainly and positively at its rated overload.

What I consider to be novel and my invention will be better understood by reference to the following speciilcation and'appended claims when considered in connection with the accompanying drawing in which Fig. 1 is a sectional view of my improved fuse; Fig. 2 is a side elevation partly in section of a modied form of the fuse; Fig. 3 is a detailed sectional view on an enlarged scale of a portion of the fuse link; Fig. 4 is a detailed sectional View on an enlarged scale of another portion of the fuselink; Fig. 5 is a side elevation ofa modified form of fuse link; and Fig. 6 is a front elevation of the fuse link of Fig..5.

Referring to the drawing, 10 indicates a fuse holder tube of insulating material open at its lower end. The upper end of fuse holder 10 is closed by a contact cap llwhich is in threaded engagement with tube 10. -A contact button 12 rests on the top of tube 10. To compensatevfor variation in the expansion and contraction oftube 10 with respect to cap 11a-nd to hold contact button'12 in engagement with tube 10, a

I spiral spring 13 is provided and located between contact cap 11 and button 12. Spring 13 insures a good electrical connection between contact button 12 and cap l1 regardless of the relatively great expansion and contraction of tube 10. Connected to button 12 is fusible element 14 which may consist of any of the well known yfusible metals, as an alloy of lead or the like. Connected to the other end of fusible element 14 is a conductor 15 which is formed of a plurality of small-diameter metal strands. Conductor 15 is formed of these very small diameter strands to provide a high degree of flexibility so that upon the operation of a fuse it may be expelled from the tube 10 without greatly resisting the expulsion action. Surrounding fusible element 14 and a short portion of conductor 15 is a thin walled small diameter tube 16 of insulating material. Tube 16 is provided closely surrounding fusible element 14 to insure operation of the fuse upon a very small overload.A Upon relatively heavy overloads tube 16 is fractured and expelled with the conductor 15. This expulsion fuse is provided primarily for combination with a switch which is adapted to open upon operation of the fuse, such .as disclosed in my copending application, Serial No. 692,414, led concurrently herewith and assigned to the same assignee. To

withstand the tension necessary to hold the switch in the closed position, a steel wire 17 is provided and connected to contact button 12 at one end and conductor 15 at the other end to thereby relieve the fusible element 14 from any tension. The resistance of steel wire 17 is so high that upon normal ilow of current through the fuse the major portion of it passes through fusible element 14. Upon the occurrence of an overload for which the fuse is designed to operate fusible element 14 is blown and the ow of current through wire 17 is immediately increased. This increased current wire 17 causes it to melt.

flow through 'I'he gases generated upon the blowing of fusible element 14 and steel wire 17 expel conductor 15 from tube 16 and out of the open end of fuse holder tube 10. Steel wire 17 is preferably formed of stainless steel to prevent any corrosive action which might cause its severing and a false operation of the fuse'upon the transmission of a tension to the fusible element 14. It is diilicult to secure a stainless steel wire to other metal parts. To insure a permanent connection of steel wire 17 to contact button 12, as best indicated in Fig.

4, a loop 18 lis made in the end of wire 17 and the end of the wire is sweated to the adjacent portion of the wire. Loop 18 is then inserted in a cylin..

drical hollow extensionl 19 in the button 12 which extends into tube of fusible element 14 is also lower end of 10. One end placed in the opening of extension 19 and the opening illled with solder.

A large amount of solder loop provided in steel wire 17 extends through the and secures it to button 12. To connect the other end of steel wire 17 to conductor 15, it is looped wound backen itself. The fusible element 14 is".

and the end v fuse.

also connected to conductor 15. About the end of conductor 15 a longitudinally split metal sleeve 20 is placed and pressed in close engagement with the conductor 15, steel wire 1'?, and fusible element 14, as better indicated in Fig. 3. Sleeve 20 ls then soldered to conductor 15 to insure a permanent connection. The provision of sleeve 20 about the upper end of conductor 15 is important as it is desirable as pointed out above to use a very flexible conductor formed with very small diameter strands twisted together. Considerable difficulty has heretofore been experienced in that upon the operation of the fuse the high pressure generated would tend to expand the end of the conductor before the inertia of the conductor was overcome in some cases resulting in the wedging of the conductor Within the small diameter tube surrounding the fusible element or in some cases wedging the conductor 15 directly in the fuse holder tube. This obviously interferes with the proper operation of the fuse and in some cases where a heavy overload occurs the fuse holder is destroyed due to the closing of the fuse holder opening and the resulting generation of a high gas pressure. The sleeve 20 holds the strands forming conductor 15 together and prevents their expansion upon the operation of the fuse. Sleeve 20 also provides a means for permanently connecting steel wire 17 to conductor 15. In Fig. 2 a modified form of fuse is shown which is designed primarily for a low current rating in which the steel wire 1'7 is able to carry the normal current passing through the In such a case, it is unnecessary to provide the fusible element 14. The operation of the fuse in this case isthe same as the operation of the fuse shown in Fig. 1 except that upon the occurrence of an overload, steel wire 1'7 is im mediately blown. In Figs. 5 and 6 a modified form of fuse link is shown which is designed for a high current rating. Difficulty has been experienced with fuse links of high current rating in providing a conductor adjacent the fusible element which will not have a high temperature rise with normal current flow causing a false operation of the fuse by melting the fusible element below the current rating of the fuse. To prevent an excessive temperature rise adjacent the fusible element 21 flat conducting strips 22 and 23 are provided and connected to opposite ends of fusible element 21. Fusible element 21 is of strip form and is soldered to strips 22 and 23. -Strip 22 may be formed integrally with contact button 24 or may be connected to it by soldering or in a similar manner. The opposite end of strip 23 is connected to a stranded conductor 25 similar to conductor 15 of the form of fuse link shown in Figs. 1 and 2. To relieve fusible element 21 of any tension steel wire 26 is provided. Loops are provided in each end of steel wire 26 which are embedded in solder on the ends of strips 22 and 23 to which fusible element 21 is connected. The solder extending through the loops in steel Wire 26 secures it to strips 22 and 23. A small diameter tube of insulating material similar to tube 16 is adapted to surround fusible element 21 in the same manner as shown in Figs. 1 and 2.

From the foregoing, it may be seen that an expulsion fuse is provided with a means for relieving the fusible element of tension which is rugged and unaffected by atmospheric conditions so that it will not deteriorate and the proper operation of the fuse on a heavy overload ls assured without the danger of damage to the fuse holder. The loops provided in the steel wire used to relieve the fusible element of tension make it possible to secure the steel wire to the adjacent parts of the fuse link.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A fuse comprising a contact button having a longitudinal opening, a wire secured in said opening, a stranded conductor secured to the other end of said wire, a split metal sleeve surrounding and closely engaging the end of said stranded conductor, and a tube of insulating material closely surrounding said Wire.

2. A fuse comprising a contact button having a longitudinal opening, a wire secured in said opening, a fusible element secured in said opening, a stranded conductor connected to the other end of said wire and said fusible element, a metal sleeve surrounding and closely engaging the end of said stranded conductor connected to said Wire and said fusible element, and a tube of insulating material closely surrounding said Wire and said fusible element.

3. A fuse link comprising a contact button, a fusible element connected to said contact button, a stranded conductor connected to the other end of said fusible element, and a steel Wire having looped ends connected to said contact button and said stranded conductors to relieve the fusible element of tension.

4. A fuse link comprising a contact button, a fusible element connected to said contact button, a stranded conductor connected to the other end of said fusible element, and a steel wire having looped ends imbedded in solder connected to the ends of said fusible element to relieve the fusible element of tension.

5. A fuse link including a fusible element and a steel wire having looped ends imbedded in solder and connected to the ends ofthe fusible element to relieve the fusible element of tension.

6. A fuse link comprising a contact button, a fiat conductor strip connected to said contact button, a fusible element connected to said strip, a second flat conductor strip connected to the other end of said fusible element, a fiexible conductor connected to said second strip, and a steel wire having looped ends imbedded in solder connected to said rst mentioned strip and said second strip to relieve the fusible element of tension.

BENJAMN R. HERMANN. 

